Bends or other irregularities in back plane pins present a serious problem in the manufacture of electronic apparatus. With current circuit pack connector technology, the number of individual electrical connections between a circuit card and the equipment back plane can number over one thousand. Typically, the connections are made between pins on the back plane spaced on 100 mil grids and matching female connectors on the circuit card edge, by the equipment user inserting the card into the appropriate slot in the equipment. Even a single pin that is bent or out of place can cause not only equipment malfunction, but also circuit destruction and customer dissatisfaction.
Inspection of the back plane for such pin irregularities is not a simple task. The pins in an individual connector are typically surrounded by a shroud, and many such connectors are mounted within a card cage. Inspection of mounted connectors, therefore, must be made from a direction parallel to the pins, and, if by humans, from several inches away from the pins. Experience has shown that such human inspection is slow, and therefore costly, requires considerable training, and yet is not very reliable.
While automated visual inspection systems for components are known, none has the ability to solve the problem addressed by this invention. U.S. Pat. No. 4,851,902, that issued Jul. 25, 1989 to Tezuka et al. discloses a system for inspecting integrated circuit lead frames. The inspection method requires precise positioning of the lead frame under test in order to align the camera image with a reference image. Positioning precise enough to detect slightly bent pins with this method would be very time consuming and defeat the advantage of automation.
U.S. Pat. No. 5,185,811, that issued Feb. 9, 1993 to Beers et al. discloses a system for observation of surface mount component leads to determine the component orientation for automated component placement. The disclosed method uses pixel summation profiles to locate leads, which show up as a substantial line of lit pixels. The method is not applicable to analyze a field of pins viewed end-on.
There is therefore a need for an inspection system for pins within shrouds mounted in card cages that is reliable, fast and inexpensive to operate. Furthermore, there is a need for an automated system in which data characterizing failed units can be easily gathered for analysis and correction.